1. Field
One embodiment of the present invention relates to a magnetic disk apparatus, and in particular, to a magnetic disk apparatus using a bit patterned medium.
2. Description of the Related Art
In current magnetic disk apparatuses (hard disk drives), bits are written to a recording layer with a magnetic head. For magnetic disks in these magnetic disk apparatuses, problems such as the interference between adjacent tracks and thermal fluctuation resistance have become serious.
Proposals have been made of bit patterned media in which a magnetic material is processed into arrayed magnetic dots separated from one another each of which is used as one bit. Such bit patterned media are expected to solve the problems such as the interference between adjacent tracks and thermal fluctuation resistance.
In current magnetic disks, one bit written by a magnetic head has an aspect ratio of about 4 to 7 and is longer in the cross track direction than in the down track direction. In such a bit pattern, if a bit aspect ratio is 4, a bit pitch is 25 nm, and the ratio of the bit length to the length of a non-recording area in the down track direction is 2:1, the interval between the bits is about 8 nm.
However, when an attempt is made to manufacture bit patterned media having a bit pattern equivalent to that of the current magnetic disks, forming magnetic dots of a high aspect ratio is very difficult and is impractical.
Thus, a proposal has been made of a bit patterned medium in which a self-assembling material is used to arrange magnetic dots in the down track direction to form magnetic dot lines so that magnetic dots in each magnetic dot line are displaced from those in the adjacent magnetic dot line by a ½ pitch. In addition, a proposal has been made that read and write be sequentially performed on magnetic dots included in a plurality of dot lines used as one track (Jpn. Pat. Appln. KOKAI Publication No. 2002-279616).
This bit patterned medium enables read and write similarly to the current magnetic disks. This eliminates the need to form magnetic dots of a high aspect ratio and provides a sufficient interval between the magnetic dots.
However, in this bit patterned medium, the amount by which the magnetic dots included in each magnetic dot line are displaced from those included in the adjacent magnetic dot line is fixed to a ½ pitch. Thus, the bit patterned medium disadvantageously cannot deal with a skew angle that may occur when the head accesses the inner or outer peripheral side of the magnetic disk.